Re: [prefix=PATCH] drivers: pmbus: core: Prevent calling pmbus_set_page with negative page

Eddie James
2017-10-25T21:23:01Z

On 10/25/2017 04:12 PM, Guenter Roeck wrote:
> On Wed, Oct 25, 2017 at 02:52:53PM -0500, Eddie James wrote:
>> From: "Edward A. James" <eajames@us.ibm.com>
>>
>> For devices with word data registers, the pmbus core may call read/write
>> word data functions with a page value of -1, in order to perform the
>> operation without setting the page. However, the read/write word data
>> functions accept only unsigned 8-bit page numbers, resulting in setting
>> a page of 0xFF in this situation. This may result in errors or undefined
>> behavior of some devices (specifically the ir35221, which allows the
>> page to be set to 0xFF, but some subsequent operations to read registers
>> may fail).
>>
> Good catch.
>
> Subject came off a bit odd.
>
> [prefix=PATCH] drivers: pmbus: core: Prevent ...
>
> Please use "[PATCH] hwmon: (pmbus/core) Prevent ..."

Yea I hit = instead of - in "--subject-prefix"...

>
> This me wonder if we should move the check into pmbus_set_page()
> instead.
>
> int pmbus_set_page(struct i2c_client *client, int page)
> {
> ...
> if (page >= 0 && page != data->currpage) {
> ...
> }
>
> What do you think ?

Yea that works well too, and reduces the code size. Though I suppose it
makes the interface slightly less intuitive, as someone might think they
can pass a value larger than u8. At least for the read/write functions,
a negative value has a meaning - "don't change the page."

Up to you, either way. I'm happy to change it.

Thanks,
Eddie

>
> Thanks,
> Guenter
>
>> Signed-off-by: Edward A. James <eajames@us.ibm.com>
>> ---
>> drivers/hwmon/pmbus/pmbus.h | 4 ++--
>> drivers/hwmon/pmbus/pmbus_core.c | 29 ++++++++++++++++++-----------
>> 2 files changed, 20 insertions(+), 13 deletions(-)
>>
>> diff --git a/drivers/hwmon/pmbus/pmbus.h b/drivers/hwmon/pmbus/pmbus.h
>> index 4efa2bd..4a16da6 100644
>> --- a/drivers/hwmon/pmbus/pmbus.h
>> +++ b/drivers/hwmon/pmbus/pmbus.h
>> @@ -405,8 +405,8 @@ struct pmbus_driver_info {
>>
>> void pmbus_clear_cache(struct i2c_client *client);
>> int pmbus_set_page(struct i2c_client *client, u8 page);
>> -int pmbus_read_word_data(struct i2c_client *client, u8 page, u8 reg);
>> -int pmbus_write_word_data(struct i2c_client *client, u8 page, u8 reg, u16 word);
>> +int pmbus_read_word_data(struct i2c_client *client, int page, u8 reg);
>> +int pmbus_write_word_data(struct i2c_client *client, int page, u8 reg, u16 word);
>> int pmbus_read_byte_data(struct i2c_client *client, int page, u8 reg);
>> int pmbus_write_byte(struct i2c_client *client, int page, u8 value);
>> int pmbus_write_byte_data(struct i2c_client *client, int page, u8 reg,
>> diff --git a/drivers/hwmon/pmbus/pmbus_core.c b/drivers/hwmon/pmbus/pmbus_core.c
>> index 302f0ae..6d6e030 100644
>> --- a/drivers/hwmon/pmbus/pmbus_core.c
>> +++ b/drivers/hwmon/pmbus/pmbus_core.c
>> @@ -186,13 +186,16 @@ static int _pmbus_write_byte(struct i2c_client *client, int page, u8 value)
>> return pmbus_write_byte(client, page, value);
>> }
>>
>> -int pmbus_write_word_data(struct i2c_client *client, u8 page, u8 reg, u16 word)
>> +int pmbus_write_word_data(struct i2c_client *client, int page, u8 reg,
>> + u16 word)
>> {
>> int rv;
>>
>> - rv = pmbus_set_page(client, page);
>> - if (rv < 0)
>> - return rv;
>> + if (page >= 0) {
>> + rv = pmbus_set_page(client, page);
>> + if (rv < 0)
>> + return rv;
>> + }
>>
>> return i2c_smbus_write_word_data(client, reg, word);
>> }
>> @@ -219,13 +222,15 @@ static int _pmbus_write_word_data(struct i2c_client *client, int page, int reg,
>> return pmbus_write_word_data(client, page, reg, word);
>> }
>>
>> -int pmbus_read_word_data(struct i2c_client *client, u8 page, u8 reg)
>> +int pmbus_read_word_data(struct i2c_client *client, int page, u8 reg)
>> {
>> int rv;
>>
>> - rv = pmbus_set_page(client, page);
>> - if (rv < 0)
>> - return rv;
>> + if (page >= 0) {
>> + rv = pmbus_set_page(client, page);
>> + if (rv < 0)
>> + return rv;
>> + }
>>
>> return i2c_smbus_read_word_data(client, reg);
>> }
>> @@ -269,9 +274,11 @@ int pmbus_write_byte_data(struct i2c_client *client, int page, u8 reg, u8 value)
>> {
>> int rv;
>>
>> - rv = pmbus_set_page(client, page);
>> - if (rv < 0)
>> - return rv;
>> + if (page >= 0) {
>> + rv = pmbus_set_page(client, page);
>> + if (rv < 0)
>> + return rv;
>> + }
>>
>> return i2c_smbus_write_byte_data(client, reg, value);
>> }
>> --
>> 1.8.3.1
>>